Technical Field
Embodiments of the invention relate generally to flame scanners for monitoring flames produced in a fossil fuel fire combustion chamber and, more particularly, to a system, method and apparatus for adjusting the field of view of a flame scanner.
Discussion of Art
A flame scanner monitors the combustion process in a fossil fuel fired combustion chamber to provide a signal indicating the presence or absence of a stable flame. With the presence of a stable flame, fossil fuel continues to be fed into the combustion chamber of the steam generator. In the event that the flame becomes unstable, or the flame is lost completely (known as a flame out condition), the flame scanner provides a loss of flame signal. Based upon a loss of flame signal, fossil fuel delivery to the combustion chamber can be discontinued before an undesirable unstable operating condition or flame out condition develops. In some systems, a human operator interrupts the fuel supply based upon the loss of flame signal; in other systems a burner management system (BMS) interrupts the fuel supply based upon the loss of flame signal.
Conventional flame scanners produce an electrical signal based upon a monitored flame. This resulting analog electrical signal is transmitted to processing electronics that are housed separately from the flame scanner, typically in an equipment rack located adjacent to a control room. The strength of the produced signal is typically proportional to the intensity of the monitored flame. If the signal strength falls below a lower set point, or rises above an upper set point, delivery of main fuel into the combustion chamber is interrupted. Set points are sometimes referred to as trip points.
One type of flame scanner is an ultraviolet tube flame scanner which produces a pulsed electrical output whose pulse rate is proportional to the intensity of ultraviolet light, in the range of approximately 250 to 400 nanometers, emitted by a flame. These scanners are particularly suited for monitoring gas flames since the emission from gas flames can be primarily in the ultraviolet range, with only minimal visible light emissions. Ultraviolet flame scanners based on Geiger-Müller tubes require extensive maintenance and have relatively limited operational lives as well as unstable failure modes.
Another type of flame scanner is a photodiode flame scanner. Photodiode flame scanners are the most prevalent type of flame scanner in use today in industrial application. In these flame scanners, visible light, in the range of approximately 400 to 700 nanometers, is collected from inside a combustion chamber, transmitted through a fiber optic cable, and directed onto a single photodiode to produce an electrical signal utilized by the separate processing electronics. Photodiode flame scanners are well suited for monitoring oil and coal flames, as emissions from such flames are in the visible and near infrared ranges.
Photodiode flame scanners mount on utility or industrial boilers and include two primary components. One component is a removable flame scanner assembly, i.e., a lens assembly, a flame sensor and fiber optic cable that extends between the lens assembly and the flame sensor). The flame sensor senses energy from the boiler via light transmission from the boiler flames by way of the fiber optic cable. The other component of the flame scanner includes a scanner guide pipe, which is a fixed, structural part of the boiler and disposed within the combustion chamber of the boiler. The flame scanner assembly fits into the guide pipe. Typically, existing flame scanners use one of several different lens barrel assemblies, each with fixed viewing angles. Often, however, the optimum viewing angle for a given application cannot be determined prior to installation of the flame scanner. Occasionally, an incorrect or non-optimal lens choice is made during an initial design phase of a given project, and is not discovered until commissioning, where it can cause rework and delays.
In view of the above there is a need for an adjustable flame scanner and related method that permits quick and easy adjustment of the viewing angle of a lens assembly of the flame scanner.